已知A=2B C=5A求代数式 A 4B C分之6A 2B-C-搜答案-搜狗做题网

已知a=-2/(根号7)+3,=-2(3-√7)/(9-7)=-(3-√7)=√7-3;求代数式a^3+5a^2-4a-6的值=a²(a+5)-4a-6=(7+3-6√7)(√7+2)-4√

a=√5-3,a+6=√5+3a^2+6a-3=a(a+6)-3=(√5-3)(√5+3)-3=5-9-3=-7

ac-bc+a^2-ab=c(a-b)+a(a-b)=(a-b)(a+c)=3*(-5)=-15

a=(根号5)-1a+1=√5a²+2a+1=5∴a²+2a-4=0a^3+2a^2-4a+1=a(a²+2a-4)+1=a×0+1=1

a²=a+2采用逐渐降次法a^5-5a+2=a²*a³-5a+2=(a+1)²*a-5a+2=(a²+2a+1)*a-5a+2=(3a+2)*a-5a

a^2=a+1两边平方a^4=a^2+2a+1=(a+1)+2a+1=3a+2a^5=a*a^4=a(3a+2)=3a^2+2a=3(a+1)+2a=5a+2所以a^5-5a+2=5a+2-5a+2=

a^5-5a+3=a³﹙a²＋a-1﹚－a^4＋a³-5a+3=a³﹙a²＋a-1﹚－a²﹙a²＋a-1﹚＋2a³-a&

当3a+4b=3时2（2a+b)+5(a+2b)=4a+2b+5a+10b=9a+12b=3(3a+4b)=3x3=9

3a^3+(a^2+5)(a^2-1)-5(a+1)(a-1)-6a=a^4+3a^3-a^2-6a=a^4+3a^3+a^2-2a^2-6a=a^2(a^2+3a+1)-2a^2-6a=-2a^2-

已知a²+a-1=0,求代数式a⁵-5a的值由a²+a-1=0,得a₁=(-1+√5)/2=-(1-√5)/2；a₂=(-1-√5)/2=-(1

ac-bc+a·a-ab=c(a-b)+a(a-b)=(a+c)(a-b)a-b=3b+c=-5两式相加,a+c=-2所以原式=-2*3=-6

ab/(a+b)=1/3取倒数(a+b)/ab=3a/ab+b/ab=31/b+1/a=3同理1/b+1/c=41/a+1/c=5相加2(1/a+1/b+1/c)=121/a+1/b+1/c=6通分(

解题思路：根据二次根式的意义和绝对值的定义进行判断求解解题过程：

a^2-a-1=0,∴a²-a=1∴a^3-2a+2010=a³-a²+a²-2a+2010=a(a²-a)+a²-2a+2010=a+a&

(a-4)/(a^2-9)除以1/(a-3)乘以(a^2+2a-3)/(a^2-8a+16)=(a-4)(a-3)(a-1)(a+3)/[(a+3)(a-3)(a-4)²]=(a-1)/(a

a(a-1)-(a²-b)a²-a-a²+b=5a-b=5(a^2+b^2)/2-ab=(a^2-2ab+b^2)/2=(a-b)^2/2=5^2/2=25/2

a^5-5a+2=a³×a²-5a+2=a³(a+1)-5a+2=a^4+a³-5a+2=(a²)²+a×a²-5a+2=(a+1

a²=a+1所以a⁴=(a²)²=(a+1)²=a²+2a+1=(a+1)+2a+1=3a+2所以原式=3a+2-3a+2=4

3a^3-2a^2+a-5=3*(-2)³-2*(-2)²-2-5=-24-8-2-5=-39

ac-bc+a2-ab=(a+c)(a-b)=-5*3=-15